Omega Nebula

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Omega Nebula
Emission nebula
H II region
The star formation region Messier 17.jpg
The star forming region Messier 17 was captured by the 2.2-metre telescope at La Silla Observatory.
Credit: ESO
Observation data: J2000 epoch
Right ascension 18h 20m 26s[1]
Declination−16° 10′ 36″[1]
Distance5,000-6,000 ly
Apparent magnitude (V)+6.0[1]
Apparent dimensions (V)11 arcmins
Physical characteristics
Radius11 ly
DesignationsM17, Swan Nebula,[1] Sharpless 45, RCW 160, Gum 81
See also: Lists of nebulae

The Omega Nebula, also known as the Swan Nebula, Checkmark Nebula, and the Horseshoe Nebula[1][2] (catalogued as Messier 17 or M17 or NGC 6618) is an H II region in the constellation Sagittarius. It was discovered by Philippe Loys de Chéseaux in 1745. Charles Messier catalogued it in 1764. It is located in the rich starfields of the Sagittarius area of the Milky Way.


Picture of M17 captured in narrowband by amateur astronomer Chuck Ayoub

The Omega Nebula is between 5,000 and 6,000 light-years from Earth and it spans some 15 light-years in diameter. The cloud of interstellar matter of which this nebula is a part is roughly 40 light-years in diameter and has a mass of 30,000 solar masses.[3] The total mass of the Omega Nebula is an estimated 800 solar masses.[4]

It is considered one of the brightest and most massive star-forming regions of our galaxy.[3] Its local geometry is similar to the Orion Nebula except that it is viewed edge-on rather than face-on.[5]

The open cluster NGC 6618 lies embedded in the nebulosity and causes the gases of the nebula to shine due to radiation from these hot, young stars; however, the actual number of stars in the nebula is much higher - up to 800, 100 of spectral type earlier than B9, and 9 of spectral type O,[citation needed] plus over a thousand stars in formation on its outer regions.[3] It is also one of the youngest clusters known, with an age of just 1 million years.[6]

The luminous blue variable HD 168607, located in the south-east part of the Omega nebula, is generally assumed to be associated with it; its close neighbor, the blue hypergiant HD 168625, may be too.

The Swan portion of M17, the Omega Nebula in the Sagittarius nebulosity is said to resemble a barber's pole.[7]

Early research[edit]

The first attempt to accurately draw the nebula (as part of a series of sketches of nebulae) was made by John Herschel in 1833, and published in 1836. He described the nebula as such:[2]

A second, more detailed sketch was made during his visit to South Africa in 1837. The nebula was also studied by Johann von Lamont and separately by an undergraduate at Yale College, Mr Mason, starting from around 1836. When Herschel published his 1837 sketch in 1847, he wrote:[2]

Sketches were also made by William Lassell in 1862 using his four-foot telescope at Malta, and by M. Trouvelot from Cambridge, Massachusetts and Edward Singleton Holden in 1875 using the twenty-six inch Clark refractor at the United States Naval Observatory.[2]


See also[edit]


  1. ^ a b c d e "NGC 6618". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-16.
  2. ^ a b c d Holden, Edward S. (January 1876). "The Horseshoe Nebula in Sagittarius" . Popular Science. 8: 269–281.
  3. ^ a b c Povich, M. S.; Churchwell, E.; Bieging, J.H.; Kang, M.; et al. (2009). "The Extended Environment of M17: A Star Formation History". The Astrophysical Journal. 696 (2): 1278–1306. arXiv:0902.3280. Bibcode:2009ApJ...696.1278P. doi:10.1088/0004-637X/696/2/1278.
  4. ^ "Messier 17". SEDS. 2007-08-13. Retrieved 2011-03-09.
  5. ^ . Broos, P. S.; Feigelson, E. D.; Townsley, L.K.; Getman, K.V; et al. (2007). "The Young Stellar Population in M17 Revealed by Chandra". The Astrophysical Journal Supplement Series. 169 (2): 353–385. arXiv:astro-ph/0612590. Bibcode:2007ApJS..169..353B. doi:10.1086/512068.
  6. ^ Hanson, M. M.; Howarth, I.D.; Conti, P.S. (1997). "The Young Massive Stellar Objects of M17". The Astrophysical Journal. 489 (2): 698–718. Bibcode:1997ApJ...489..698H. doi:10.1086/304808.
  7. ^ Steven Coe (2007). Nebulae and How to Observe Them. Springer Science & Business Media. p. 116. ISBN 978-1-84628-729-9.
  8. ^ "VST Captures Three-In-One". Retrieved 16 June 2017.

External links[edit]

Works related to The Horseshoe Nebula in Sagittarius at Wikisource

Coordinates: Sky map 18h 20m 26s, −16° 10′ 36″